Sample Preparation
The nutshells were cracked by a nutcracker and the kernels were isolated from the shell. The shells were then segmented by Epilog Fusion M2 laser cutter using CO2 laser and subsequently sanded to a required uniform dimension. Sanding the cross-sectional areas also helps to remove the laser-induced localized burned regions. The inner and outer surface of the shells were also sanded partially to mitigate uneven surface of the shell morphology. The samples obtain a uniform form, making them suitable for application into numerous practical devices. Samples were then cleaned with ultrapure water. Nutshell samples were immersed in a solution consisting of 40% (v/v) acetone, 30% (v/v) ethanol, and 30% (v/v) deionized (DI) water. The mixture was heated at 70 °C for 20 minutes to break the lignin and hemicellulose network. Samples were rinsed thoroughly with ultra-pure water to eliminate the residues. Following the treatments the samples were dried in a tube furnace at 100 °C for 1 h under a constant flow of nitrogen gas. After being dried in the ambient environment for 24 h, the samples are marked as Almond Shell - AS, Filbert Shell - FS, Pecan Shell - PS, and Walnut Shell - WS. To enhance the hydrophilicity, a few of the samples were further plasma cleaned for 8 minutes.